It’s been more than a decade since the ancient rock city of Petra made its silver-screen debut in Indiana Jones and the Last Crusade. Petra was an ideal backdrop for the action-packed movie. However, Hollywood overlooked what is perhaps Jordan’s second most-important archaeological secret — its desert castles.

About 75 percent of this Middle Eastern country, which is roughly the size of Portugal, consists of dry and barren lands. The black basalt desert east of the capital city of Amman is a seemingly endless and empty expanse wedged between Syria to the north, Iraq to the east, and Saudi Arabia to the east and south. It’s mostly flat, and dotted with low-growing shrubs, bushes and cacti.

The Qasr Azraq fortress is enclosed by walls that are approximately 260 feet long (80 m).

There are few proper roads here, but dozens of desert tracks that crisscross the parched landscape. They have been used for centuries by pilgrims en route to Mecca, by caravans carrying goods from one trading post to another and by caliphs on their way to their royal retreats.

Forlorn in a vast arid sea, imposing desert castles and pavilions stood their ground as islands of civilization. Most of them were built during the Umayyad period, the first major Islamic dynasty, which reigned from A.D. 661-750.

As lonely as these bastions of civilization appear today — often located many miles from human settlement — they were at one time integrated agricultural and commercial complexes, well-watered townships situated at the edge of the desert.

Often constructed on top of and incorporating earlier Roman and Nabatean structures, these imposing palace-fortresses served many purposes. The magnificent desert pavilions could be used for defense, if necessary. But they were primarily places where the Umayyad caliphs could, to quote our guide Mohamed, “get away from it all,” leaving the cares of ruling behind and retreating here to hunt and hawk, relax in secluded baths, meet with tribal groups over whom they ruled, and occasionally offer hospitality to caravans passing through.

With just one day to spare for a desert excursion while staying in Amman, I had to select three of the many desert castles.

Qasr Kharana (qasr means palace or castle in Arabic), located about 37 miles (60 km) east of Amman, is one of the closest and easiest of the desert castles to reach from the capital. It’s also one of the oldest, probably built prior to A.D. 710, as an inscription found on one of the interior doorways suggests. Qasr Kharana is considered to be an important example of early Islamic art and architecture.

From the outside, Kharana looks like a perfect mini-fortress, with almost circular tower buttresses at each corner and semi-circular towers in each of the walls except for the entrance wall, where a pair of towers flank the massive entry.

Appearances can sometimes be deceiving, as inside, utilitarian stables and storage rooms surround a central courtyard on the ground level, and the upper floor of this desert castle is anything but fortress-like.